1. Technical Field of the Invention
Multiple tube processing coil for processing two or more elements that are ring-shaped in the processing zone thereof, are made of electrically conductive material, and each continuously encompass the pressing zone of a mating piece, said multiple tube processing coil comprising a pulsed power source and an electric conductor that is connected thereto and entirely surrounds the elements in the processing zone thereof.
This method is known as electromagnetic pulse joining. It utilizes the force of a magnetic field to deform axially symmetrical workpieces of conductive material, such as tubes and rings. As a tool for this there serves a coil, through which a current flows and in the interior of which a magnetic field loads the workpiece beyond its flow limit, thereby deforms it and in this way presses it against the surface of the mating piece to the workpiece.
A known application, for example, is to fix a tubular filling nozzle on the neck of a petrol tank by crimping. Another, known application is the production of a tow bar for motor vehicles. To this end, an aluminum tube is joined by electromagnetic pulse joining to two steel coupling pieces.
2. Description of the Prior Art
In this and other applications, a coil surrounds the object, made of electrically conductive material, which is to be deformed, at a small distance. When an electric current flows through this coil, a magnetic field forms, which encloses the element to be deformed, and therein induces eddy currents in its surface, which in turn generate a second magnetic field with a direction opposite to the first, for which reason the two fields repel one another. Thereby, on the circumference of the workpiece, in the plane of the electric coil, a force develops which is oriented radially to the center point of the workpiece.
If this force is large enough to exceed the limit of elastic deformability of the workpiece, it is permanently deformed. Since this limits only needs to be exceeded once and only for a very short time, it is appropriate to use a current source, which emits the energy in pulses, for example a so-called capacitor bank, which consists of a multiplicity of capacitors connected to one another. These capacitors are continuously charged without load and then, via a switch, suddenly connected to a coil, which surrounds the workpiece. In the prior art, current values of 150,000-500,000 amperes are reached. Such high currents discharge the capacitor bank in a very short time, a typical value from the prior art is 45 microseconds.
While the current is flowing, it builds up such a high magnetic flux that the secondary magnetic field generated in the workpiece, which is oriented inversely to the generating primary magnetic field, generates, due to its reaction force, such high forces that the wall of the workpiece is accelerated to peak velocities up to 500 meters per second, and is thereby deformed.
In the process, it is also possible to deform multiple elements, which are inserted concentrically one inside the other and contact one another mutually or are at least at a very small distance from one another. Here, the deforming effect is greatest on the outermost of all the elements.
The nearest, inner element is then principally deformed by the mechanical effect of the outer element. In comparison to this, in most cases, depending on the wall thickness and the mechanical conductivity of the outer element, the magnetic effect on the elements disposed more inwardly is very small or may even lie below the deformation limit, because most of the magnetic energy has already been consumed in the outer element to develop eddy currents.
Therefore, in this manner, elements of another, deformable and non-electromagnetically conducting material, such as plastic, may be introduced within an element of magnetically conductive material. These intermediate rings can be used as simulators or as sealing rings.
However, this, in principle, very simple process has certain problems and restrictions for its successful realization, which are described, inter alia, in U.S. Pat. No. 4,150,274.
Since the internal diameter of the coil should be only slightly larger than the outer diameter of the workpiece, a manufacturer who wants to use the EMPB process requires various examples of the expensive coils.
A further disadvantage is that this coil can only process one workpiece at a time. Since the workpiece must be positioned very accurately in the coil, the feeding and discharge of the device takes much more time than the joining process itself.
Another problem of the prior art is the size of the coil, in particular when multiple workpieces are to be processed simultaneously in one device, the space required by the coils is greater than that for the workpieces.
Another disadvantage is that coils with a multiplicity of windings are advantageous for adapting to the currently available capacitors with typically very high voltages. The disadvantage of such a multi-winding coil, however, is that the individual windings are supported on one another while the current is flowing and must withstand the same high reaction force that causes permanent deformations in the workpiece. That may lead to the conductors of the coil touching one another and thereby stripping off or striking off their insulation, such that short circuits may occur and the coil may become unusable.
Hitherto known coils for the electromagnetic pulse crimping method are generally complicated to manufacture and wear very rapidly compared to other machinery in joining technology.